The present invention relates to a method for the manufacture of an IC-processed micro electro-static motor, and more particularly to a method for manufacturing an IC-processed micro electro-static motor which is provided with a curved bearing structure to significantly decrease the frictional torque of the micro electro-static motor, and an on-chip detection device to facilitate the micromotor rotational speed detection.
Some publications, for example W. S. Trimmer and K. J. Gabriel, "Design Considerations for a Practical Electrostatic Micromotor", Sensors and Actuators, 11 (1987), pp. 189-206, and S. F. Bart et al., "Design Considerations for Microfabricated Electric Actuators", Sensors and Actuators, 14 (1988), pp. 269-292, have discussed possible designs for micromotors based on electrostatic-drive principles. In recent years, there has been a continuous development of silicon surface micromachining technology. Some micro-mechanical devices, such as micro-turbines and micro electro-static motors, which are not accessible by conventional machining technologies have been successfully made out by using technology derived from IC (integrated-circuit) manufacturing processes. For example, the literature, L. S. Fan et al., "IC-processed Electrostatic Micromotors", Sensors and Actuators, vol. 20, pp. 41-47, 1989, describes the design, fabrication and operation of several electrostatically driven rotating motors, including the stepping micromotors and the synchrohous micromotors, that have been produced by using integrated-circuit processing. The literature, M. Mehregany et al., "Measurement of Wear in Polysilicon Micromotors", IEEE Trans. Electron Devices, Vol. 39, No. 5, pp. 1136-1143, May 1992, describes two polysilicon variable-capacitance rotary side-drive micromotor types, including harmonic (or wobble) and salient-pole, that are produced by IC microfabrication technology.
One of the important issues in the design of micromotor structures design is how to reduce friction and surface sticking between the rotor and the bearing (or hub). It is found that the contact of the rotor and the bearing in the prior art is a surface contact or plane contact, resulting in a relatively large frictional torque for the micromotor. In addition, a relatively complicated measurement system, such as a video camera system or laser-based measurement system, is inevitably needed to detect the rotational speed of the conventional micromotor. The laser-based measurement system is detailed in K. J. Gabriel et al., "In situ Friction and Wear Measurements in Integrated Polysilicon Mechanisms", Sensors and Actuators, A21-A23 (1990), pp. 184-188. Thus, how to improve the method of detecting micromotor rotational speed is also an important issue in this art.